This invention relates to control of a diesel engine equipped with a variable capacity turbocharger and an exhaust recirculation device.
Tokkai Hei 7-139413 published by the Japanese Patent Office in 1995 discloses a control method of a diesel engine equipped with a turbocharger and an exhaust gas recirculation (EGR) device. The EGR device comprises an EGR valve which regulates an EGR amount. The control method determines a turbocharging region and an EGR region according to a load and rotation speed of the engine.
xe2x80x9cSimulation of a variable geometry turbocharged-diesel engine for control algorithm developmentxe2x80x9d, C524/127/97 published by the United Kingdom Institution of Mechanical Engineers (IMechE) in 1997 discloses a control method for controlling the EGR amount and an opening of a variable nozzle of the turbocharger in a transient state of the diesel engine.
xe2x80x9cEGR System in a Turbocharged Diesel Enginexe2x80x9d, pp. 193-196, Technical Preprints, published by the Japan Institute of Automobile Technology in October, 1996, discloses control of the EGR amount of the EGR device by varying the opening area of the variable nozzle of the turbocharger.
In some of the prior art techniques, when the EGR amount is varied, the supercharging pressure of the turbocharger is maintained constant, and when the variation of turbocharging pressure is performed, the EGR amount is maintained constant.
However, when the EGR amount is varied, the turbocharging pressure will vary, and when the turbocharging pressure is varied, the EGR amount will also vary because the exhaust pressure varies. That is, the turbocharging pressure and the EGR amount affect each other. Therefore, if it is attempted to keep the turbocharging pressure constant when varying the EGR amount, the opening of the variable nozzle of the turbocharger must be readjusted. Moreover, if it is attempted to keep the EGR amount constant when the turbocharging pressure is varied, the opening of the EGR valve must be readjusted.
This control works effectively when the engine is operated in a steady state, but it does not work well in the transient state when running conditions of the engine vary. Further, if the opening of the variable nozzle and the opening of the EGR valve are changed simultaneously, the change in one of the turbocharging pressure and EGR amount may result in a disturbance in the control of the other.
In a diesel engine, the turbocharging pressure and the EGR amount affect the amount of noxious substances in the exhaust gas, so both the turbocharging pressure and the EGR amount must be controlled to optimum values in order to reduce the amount of noxious substances. However, it is difficult to control the EGR amount and the turbocharging pressure to optimum values for the above-mentioned reason, especially in the transient state of the engine.
It is therefore an object of this invention to precisely control the EGR amount according to the turbocharging pressure based on a differential pressure upstream and downstream of the EGR valve and the EGR amount as parameters.
In order to achieve the above objects, this invention provides a control device for an engine. The engine comprises an intake passage, an exhaust passage and a turbocharger having an exhaust gas turbine in the exhaust passage, and an exhaust gas recirculation valve which recirculates part of an exhaust gas in the exhaust passage upstream of the exhaust gas turbine to the intake passage. The turbocharger turbocharges an intake air in the intake passage according to a rotation of an exhaust gas turbine, and the exhaust gas turbine has an adjusting mechanism of a cross-sectional area of an exhaust gas flow in the exhaust gas turbine.
The control device comprises a sensor which detects a running condition of the engine, a sensor which detects the cross-sectional area, and a microprocessor programmed to determine a target recirculation amount of the exhaust gas recirculation valve according to the running condition, calculate a target control value of the exhaust gas recirculation valve based on the target recirculation amount and the cross-sectional area, and control the exhaust gas recirculation valve according to the target control value.
This invention also provides a control device comprising a mechanism for detecting a running condition of the engine, a mechanism for detecting the cross-sectional area, a mechanism for determining a target recirculation amount of the exhaust gas recirculation valve according to the running condition, a mechanism for calculating a target control value of the exhaust gas recirculation valve based on the target recirculation amount and the cross-sectional area, and a mechanism for controlling the exhaust gas recirculation valve according to the target control value.
This invention also provides control method for an engine comprising the steps of detecting a running condition of the engine, detecting the cross-sectional area, determining a target recirculation amount of the exhaust gas recirculation calculating a target control value of the exhaust gas recirculation valve based on the target recirculation amount and the cross-sectional area, and controlling the exhaust gas recirculation valve according to the target control value.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.